1. Technical Field of the Invention
The present invention relates generally to a composite gas sensor which may be employed in an air-fuel ratio control system measuring the concentrations of different components contained in exhaust gasses of an internal combustion engine of automotive vehicles, and more particularly to an improvement on an electric connector used in such a composite gas sensor.
2. Background Art
Gas sensors equipped with a sensor element made up of a laminated plate are known for use in burning control of fuel in internal combustion engines of modern automotive vehicles. Gas sensors of this type generally have disposed therein a connector electrically coupled through leads to electrodes provided on the sensor element for use in picking up a sensor output and supplying the power to a heater provided on the sensor element. The leads extend outside the gas sensor and connect with an external device.
In recent years, there is an increasing need for composite sensor elements. The composite sensor elements are each designed to measure concentrations of different gas components simultaneously. For instance, in a case of automotive vehicles, the composite sensor element is used to measure NOx and O2 contents and an air-fuel ratio of exhaust gasses simultaneously. For precise measurement, composite sensor elements equipped with a plurality of electrochemical cells are being used. Sensor elements of this type must have many electrodes for the cells.
However, if a sensor element of the above type is installed in a gas sensor equipped with a connector such as one taught in Japanese Utility Model Second Publication No. 8-1493, a drawback is encountered in that it is difficult to establish firm engagement of the connector with electrodes of the sensor element, which may result in electric disconnections of the connector and the electrodes.
The gas sensor as taught in the above publication includes electrode terminals provided on an end of the sensor element remote from a sensing portion, a metallic sensor element holder, a receptacle leading to the electrode terminals, a ceramic housing having disposed therein the receptacle in isolation from the holder, a spring, and a staking ring pressing a spring to produce a spring pressure for holding leads. The staking ring has extensions formed around the periphery thereof which make a connection of the staking ring and an end portion of the holder. Therefore, there are drawbacks in that the use of the staking ring increases production costs and results in complexity of assembly of the gas sensor.
Japanese Utility Model First Publication No. 61-70763 discloses a gas sensor which includes an insulation porcelain, four spring plates disposed in the insulation porcelain, and a sensor element having electrode terminals. The sensor element is mounted in the insulation porcelain in electric contact with the spring plates. The sensor element has two of the electrode terminals provided on one surface thereof because it is difficult to provide three or more electrode terminals on one surface for a narrow internal space of the insulation porcelain.
It is therefore a principal object of the invention to avoid the disadvantages of the prior art.
It is another object of the invention to provide an improved structure of a gas sensor constructed to make firm electric connections between electrode terminals of a sensor element and a connector and to be assembled easily.
According to one aspect of the invention, there is provided a gas sensor which comprises: (a) a hollow cylindrical housing; (b) a sensor element made of a laminated plate which includes sensing portion and a base portion opposite the sensing portion and which has an array of electrode terminals formed on each of opposed surfaces of the base portion, the sensor element being retained at an sensing portion thereof by an insulation porcelain within the housing; (c) a cover covering the base portion of the sensor element; and (d) a connector disposed within the cover, the connector having arrays of terminals which each array is connected electrically to one of the arrays of electrode terminals of the sensor element, each of the terminals including a contact which is elastically deformable at least in a direction substantially perpendicular to the opposed surfaces of the sensor element to establish a firm electric connection to one of the electrode terminals of the sensor element.
In the preferred mode of the invention, the connector also includes insulating members. A retaining spring member is further disposed within the cover to elastically retain each of the arrays of terminals of the connector through one of the insulating members so as to urge the terminals of the connector into constant contact with the electrode terminals of the sensor element.
The insulating members are made of one of a ceramic material and a resin material.
The connector may have two terminal arrays each made up of four terminals making the electric connections to the electrode terminals of the sensor element, respectively.
An elastic pressure produced by the retaining spring member to urge the terminals of the connector into constant contact with the electrode terminals of the sensor element is set greater than or equal to a total of elastic pressures produced by elastic deformation of the contacts of the terminals of the connector in the direction perpendicular to the opposed surfaces of the sensor element.
The elastic pressure produced by the elastic deformation of the contacts of the terminals of the connector is so set as to absorb a gap between each of the contacts and a corresponding one of the electrode terminals of the sensor element.
Each of the insulating members has an inner wall opposed to one of the surfaces of the sensor element, an end wall facing a tip of the sensing portion of the sensor element, and an outer wall opposite the inner wall. Each of the terminals of the connector is curved in the shape of C so as to surround the inner wall, the end wall, and the outer wall of one of the insulating members.
Each of the terminals of the connector is made of one of a round conductive line and a rectangular conductive line.
Each of the terminals of the connector may have a hook fitted on an end of one of the insulating members so that half of the terminals are arrayed on the surface of one of the insulating members.
A second hollow insulation porcelain is further disposed within the cover. The retaining spring member includes a holding portion and a retaining portion. The holding portion holds the terminals of the connector through the insulating members. The retaining portion is placed in elastic engagement with an inner wall of the second hollow insulation porcelain so as to urge the terminals of the connector into constant contact with the electrode terminals of the sensor element.